Littelfuse LFUIDSR100 100A 600VAC/600VDC Class RK5 Fuse is the first indicating power fuse ever. Its solid-state design provides state-of-the-art reliability; it will forever change the way you look at modern circuit protection. Money is wasted each time a circuit opens and halts production. Thousands of dollars can be lost with every minute spent testing to discover the cause. The Littelfuse IDSR Indicator™ fuse offers you a better way. Just a simple glance a the IDSR Indicator’s window tells which circuit is open. The circuit can be tested and any problem corrected without unnecessary delay. No time wasted finding the faulted circuit. No system damage. And no costly down time.